The invention relates more particularly to a brake master cylinder for a motor vehicle, of the type which comprises an essentially axial body inside a bore of which is slideably mounted at least one axial piston which is capable of being actuated by a driver of the vehicle between a rear position of rest and a forward position of application of a braking force, and which is returned elastically to its rear position of rest against a stop formed in the body, of the type in which the bore comprises two sealing means, front and rear, which are interposed between the piston and the bore, the front sealing means delimiting. In the bore, a rear supply chamber and a front pressure chamber, of the type in which the body comprises a radial supply duct which connects an external reservoir of hydraulic fluid to the rear supply chamber and which opens between the two sealing means, of the type in which the body has a drilling for supplying a braking circuit which opens into the front pressure chamber, of the type which comprises means for placing the front pressure chamber and the rear supply chamber in communication, which means are capable of being inhibited by the piston when it is moved axially forward towards its position of application in order to isolate the front pressure chamber from the rear supply chamber and thus allow a braking pressure to become established in the front pressure chamber.
Numerous examples of brake master cylinders of this type are known.
In most master cylinders of this type, at least one of the two sealing means is carried by the piston. It is therefore subjected to significant wear because of the reciprocating movement that this piston performs in the bore of the body of the booster during successive braking operations.
This wear is likely to compromise the sealing of the supply and pressure chambers of the booster, which may have even more serious consequences given that most current master cylinders are designed to have large piston cross sections so as to be able to produce a high braking pressure.